Method and apparatus for improved planar and dc modes for non-zero reference lines

ABSTRACT

A method of video decoding includes retrieving, from a coded video bitstream for a current block encoded in an intra prediction mode, a reference line index indicating a reference line from a plurality of reference lines that include a zero reference line. The method includes determining whether the current block is encoded in a non-angular intra prediction mode. The method includes, in response to the block being encoded in the non-angular intra prediction mode, determining whether the reference line index indicates a non-zero reference line from the plurality of reference lines. The method includes in response to determining that the reference line index is the non-zero reference line, (i) enabling non-angular intra prediction modes for the non-zero reference line, and (ii) decoding the current block with at least one reference sample from the non-zero reference line.

INCORPORATION BY REFERENCE

This present disclosure claims the benefit of priority to U.S.Provisional Application No. 62/822,027, “IMPROVED PLANAR AND DC MODESFOR NON-ZERO REFERENCE LINES” filed on Mar. 21, 2019, which isincorporated by reference herein in its entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

A video encoder and decoder can utilize techniques from several broadcategories, including, for example, motion compensation, transform,quantization, and entropy coding.

Video codec technologies can include techniques known as intra coding.In intra coding, sample values are represented without reference tosamples or other data from previously reconstructed reference pictures.In some video codecs, the picture is spatially subdivided into blocks ofsamples. When all blocks of samples are coded in intra mode, thatpicture can be an intra picture. Intra pictures and their derivationssuch as independent decoder refresh pictures, can be used to reset thedecoder state and can, therefore, be used as the first picture in acoded video bitstream and a video session, or as a still image. Thesamples of an intra block can be exposed to a transform, and thetransform coefficients can be quantized before entropy coding. Intraprediction can be a technique that minimizes sample values in thepre-transform domain. In some cases, the smaller the DC value after atransform is, and the smaller the AC coefficients are, the fewer thebits that are required at a given quantization step size to representthe block after entropy coding.

Traditional intra coding such as known from, for example MPEG-2generation coding technologies, does not use intra prediction. However,some newer video compression technologies include techniques thatattempt, from, for example, surrounding sample data and/or metadataobtained during the encoding/decoding of spatially neighboring, andpreceding in decoding order, blocks of data. Such techniques arehenceforth called “intra prediction” techniques. Note that in at leastsome cases, intra prediction is only using reference data from thecurrent picture under reconstruction and not from reference pictures.

There can be many different forms of intra prediction. When more thanone of such techniques can be used in a given video coding technology,the technique in use can be coded in an intra prediction mode. Incertain cases, modes can have submodes and/or parameters, and those canbe coded individually or included in the mode codeword. Which codewordto use for a given mode/submode/parameter combination can have an impactin the coding efficiency gain through intra prediction, and so can theentropy coding technology used to translate the codewords into abitstream.

A certain mode of intra prediction was introduced with H.264, refined inH.265, and further refined in newer coding technologies such as jointexploration model (JEM), versatile video coding (VVC), and benchmark set(BMS). A predictor block can be formed using neighboring sample valuesbelonging to already available samples. Sample values of neighboringsamples are copied into the predictor block according to a direction. Areference to the direction in use can be coded in the bitstream or mayitself be predicted.

Referring to FIG. 1A, depicted in the lower right is a subset of ninepredictor directions known from H.265's 33 possible predictor directions(corresponding to the 33 angular modes of the 35 intra modes). The pointwhere the arrows converge (101) represents the sample being predicted.The arrows represent the direction from which the sample is beingpredicted. For example, arrow (102) indicates that sample (101) ispredicted from a sample or samples to the upper right, at a 45 degreeangle from the horizontal. Similarly, arrow (103) indicates that sample(101) is predicted from a sample or samples to the lower left of sample(101), in a 22.5 degree angle from the horizontal.

Still referring to FIG. 1A, on the top left there is depicted a squareblock (104) of 4×4 samples (indicated by a dashed, boldface line). Thesquare block (104) includes 16 samples, each labelled with an “S”, itsposition in the Y dimension (e.g., row index) and its position in the Xdimension (e.g., column index). For example, sample S21 is the secondsample in the Y dimension (from the top) and the first (from the left)sample in the X dimension. Similarly, sample S44 is the fourth sample inblock (104) in both the Y and X dimensions. As the block is 4×4 samplesin size, S44 is at the bottom right. Further shown are reference samplesthat follow a similar numbering scheme. A reference sample is labelledwith an R, its Y position (e.g., row index) and X position (columnindex) relative to block (104). In both H.264 and H.265, predictionsamples neighbor the block under reconstruction; therefore no negativevalues need to be used.

Intra picture prediction can work by copying reference sample valuesfrom the neighboring samples as appropriated by the signaled predictiondirection. For example, assume the coded video bitstream includessignaling that, for this block, indicates a prediction directionconsistent with arrow (102)—that is, samples are predicted from aprediction sample or samples to the upper right, at a 45 degree anglefrom the horizontal. In that case, samples S41, S32, S23, and S14 arepredicted from the same reference sample R05. Sample S44 is thenpredicted from reference sample R08.

In certain cases, the values of multiple reference samples may becombined, for example through interpolation, in order to calculate areference sample; especially when the directions are not evenlydivisible by 45 degrees.

The number of possible directions has increased as video codingtechnology has developed. In H.264 (year 2003), nine different directioncould be represented. That increased to 33 in H.265 (year 2013), andJEMNVC/BMS, at the time of disclosure, can support up to 65 directions.Experiments have been conducted to identify the most likely directions,and certain techniques in the entropy coding are used to represent thoselikely directions in a small number of bits, accepting a certain penaltyfor less likely directions. Further, the directions themselves cansometimes be predicted from neighboring directions used in neighboring,already decoded, blocks.

The intra prediction modes used in HEVC are illustrated in FIG. 1B. InHEVC, there are total 35 intra prediction modes, among which mode 10 ishorizontal mode, mode 26 is vertical mode, and mode 2, mode 18 and mode34 are diagonal modes. The intra prediction modes are signalled by threemost probable modes (MPMs) and 32 remaining modes.

FIG. 1C illustrates the intra prediction modes used in VVC. In VVC,there are total 95 intra prediction modes as shown in FIG. 1C, wheremode 18 is the horizontal mode, mode 50 is the vertical mode, and mode2, mode 34 and mode 66 are diagonal modes. Modes −1˜−14 and Modes 67˜80are called Wide-Angle Intra Prediction (WAIP) modes.

The mapping of intra prediction directions bits in the coded videobitstream that represent the direction can be different from videocoding technology to video coding technology; and can range, forexample, from simple direct mappings of prediction direction to intraprediction mode, to codewords, to complex adaptive schemes involvingMPMs, and similar techniques. In all cases, however, there can becertain directions that are statistically less likely to occur in videocontent than certain other directions. As the goal of video compressionis the reduction of redundancy, those less likely directions will, in awell working video coding technology, be represented by a larger numberof bits than more likely directions.

SUMMARY

According to an exemplary embodiment, a method of video decodingperformed in a video decoder includes receiving a coded video bitstreamincluding a current block in a current picture. The method includesretrieving, from the coded video bitstream for the current block encodedin an intra prediction mode, a reference line index indicating areference line from a plurality of reference lines that include a zeroreference line, wherein the zero reference line comprises a closerreference line to the current block than each other non-zero referenceline in the plurality of reference lines. The method includesdetermining whether the current block is encoded in a non-angular intraprediction mode. The method includes, in response to the block beingencoded in the non-angular intra prediction mode, determining whetherthe reference line index indicates a non-zero reference line from theplurality of reference lines. The method includes in response todetermining that the reference line index is the non-zero referenceline, (i) enabling non-angular intra prediction modes for the non-zeroreference line, and (ii) decoding the current block with at least onereference sample from the non-zero reference line.

According to an exemplary embodiment, a video decoder for video decodingincludes circuitry configured to receive a coded video bitstreamincluding a current block in a current picture. The circuitry is furtherconfigured to retrieve, from the coded video bitstream for the currentblock encoded in an intra prediction mode, a reference line indexindicating a reference line from a plurality of reference lines thatinclude a zero reference line, wherein the zero reference line comprisesa closer reference line to the current block than each other non-zeroreference line in the plurality of reference lines. The circuitry isfurther configured to determine whether the current block is encoded ina non-angular intra prediction mode. The circuitry is further configuredto, in response to the block being encoded in the non-angular intraprediction mode, determine whether the reference line index indicates anon-zero reference line from the plurality of reference lines. Thecircuitry is further configured to, in response to a determination thatthe reference line index is the non-zero reference line, (i) enablenon-angular intra prediction modes for the non-zero reference line, and(ii) decode the current block with at least one reference sample fromthe non-zero reference line.

According to an exemplary embodiment, a non-transitory computer readablemedium having instructions stored therein, which when executed by aprocessor in a video decoder causes the processor to execute a methodthat includes retrieving, from the coded video bitstream for the currentblock encoded in an intra prediction mode, a reference line indexindicating a reference line from a plurality of reference lines thatinclude a zero reference line, wherein the zero reference line comprisesa closer reference line to the current block than each other non-zeroreference line in the plurality of reference lines. The method includesdetermining whether the current block is encoded in a non-angular intraprediction mode. The method includes, in response to the block beingencoded in the non-angular intra prediction mode, determining whetherthe reference line index indicates a non-zero reference line from theplurality of reference lines. The method includes in response todetermining that the reference line index is the non-zero referenceline, (i) enabling non-angular intra prediction modes for the non-zeroreference line, and (ii) decoding the current block with at least onereference sample from the non-zero reference line.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1A is a schematic illustration of an exemplary subset of intraprediction modes;

FIG. 1B is an illustration of exemplary intra prediction directions.

FIG. 1C is an illustration of exemplary intra prediction directions.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is a schematic illustration of a current block and itssurrounding neighbors.

FIG. 9 is a schematic illustration of a current block with multiplereference lines in accordance with an embodiment.

FIG. 10 is a schematic illustration of a current block with multiplereference lines and corresponding reference sample positions fornon-angular intraprediction modes in accordance with an embodiment.

FIG. 11 is a schematic illustration of a current block with multiplereference lines and corresponding reference sample positions fornon-angular intraprediction modes in accordance with an embodiment.

FIG. 12 is a schematic illustration of a current block with multiplereference lines and corresponding reference sample positions fornon-angular intraprediction modes in accordance with an embodiment.

FIG. 13 is an illustration of an embodiment of a process performed by adecoder.

FIG. 14 is a schematic illustration of a computer system in accordancewith an embodiment of the present disclosure.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4. The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4. Brieflyreferring also to FIG. 4, however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6.

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7.

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

According to some embodiments, to code a block in intra mode using HEVC,a most probable mode (MPM) list of size 3 is built based on the intramodes of the neighboring blocks. This MPM list may be referred to as theMPM list or primary MPM list. If the intra mode is not from the MPMlist, a flag is signalled to indicate whether intra mode belongs to theselected modes.

An embodiment of the MPM list generation process for HEVC is shown inAppendix 1, where leftIntraDir is used to indicate the mode in the leftblock and aboveIntraDir is used to indicate the mode in the above block.If left or block is currently not available, leftIntraDir oraboveIntraDir will be set to DC_IDX. In addition, variables “offset ”and “mod” are constant values, which are set to 29 and 32 respectively.

According to some embodiments, a size of the MPM list in VVC is setequal to 6 for both an adjacent reference line (e.g., zero referenceline) and non-adjacent reference lines (e.g., non-zero reference lines).The positions of neighboring modes used to derive 6 MPM candidates mayalso be the same for adjacent and non-adjacent reference lines, which isillustrated in FIG. 8. In FIG. 8, the block A and block B denote theabove and left neighboring coding unit of a current block 800, andvariables candIntraPredModeA and candIntraPredModeB indicate theassociated intra prediction modes of block A and B, respectively.Variables candIntraPredModeA and candIntraPredModeB may initially be setequal to INTRA_PLANAR. If block A (or B) is marked as available,candIntraPredModeA (or candIntraPredModeB) may be set equal to theactual intra prediction mode of block A (or B).

The MPM candidate derivation process may be different for the adjacentand non-adjacent reference lines. For example, for a zero referenceline, if the modes for the two neighboring blocks are Planar or DC mode,default modes are used to construct the MPM list, where the first twocandidates are the Planar and DC modes, and the remaining four modes areangular modes (e.g., angular default modes). For non-zero referencelines, if the modes of the two neighboring blocks are Planar or DC mode,6 angular default modes may be used to construct the MPM list. Anembodiment of the MPM list derivation process is shown in Appendix 2,where candModeList[x] with x=0 . . . 5 denotes the 6 MPM candidates,IntraLumaRefLineIdx[xCb][yCb] denotes the reference line index of theblock to be predicted, and IntraLumaRefLineIdx[xCb][yCb] can be 0, 1, or3. In some examples, a unified intra mode coding approach is implementedwhere the planar mode is put as the first MPM.

Multi-line intra prediction uses more than one reference lines for intraprediction, where the encoder decides and signals which reference lineis used to generate the intra predictor. In some examples, the referenceline index is signaled before intra prediction modes, and only the mostprobable modes are allowed in case a nonzero reference line index issignaled. In FIG. 9, for a current block (900), an example of 4reference lines is depicted (e.g., Reference Line 0, Reference Line 1,Reference Line 2, Reference Line 3), where each non-zero reference lineis composed of six segments (e.g., Segment A to F), together with thetop-left reference sample (i.e., sample between Segment C and SegmentF). As illustrated in FIG. 9, each reference line includes a row abovethe current Block (900) and a row that is left of the Current block(900). In some examples, Segment A and F are padded with the closestsamples from Segment B and E, respectively.

In some coding schemes (e.g., VTM4.0), since only angular MPMs are usedfor non-zero reference lines, and the MPM list for the zero-referenceline is not directly used for non-zero reference lines, multiple MPMlist generation processes for different cases are required. Usingmultiple MPM list generation processes due to the fact that only angularMPMs are used for non-zero reference lines is inefficient andundesirable.

The embodiments of the present disclosure may be used separately orcombined in any order. Further, each of the methods, encoder and decoderaccording to the embodiments of the present disclosure may beimplemented by processing circuitry (e.g., one or more processors or oneor more integrated circuits). In one example, the one or more processorsexecute a program that is stored in a non-transitory computer-readablemedium. According to embodiments of the present disclosure, the termblock may be interpreted as a prediction block, a coding block, or acoding unit (i.e., CU).

According to some embodiments, the line index of the nearest referenceline is 0 (i.e., zero reference line), and the other lines are callednon-zero reference lines. In some examples, the variable candModeListdenotes the MPM list, RefLineldx denotes the reference line index of acurrent block, and candlntraPredModeA and candlntraPredModeB denote theleft and above neighboring modes, respectively. In some embodiments, ifone neighboring mode is not the Planar or DC mode, or one neighboringmode is generating prediction samples according a given predictiondirection, such as intra prediction mode 2≠66 as defined in current VVCdraft 2, this mode is called an angular mode. In some embodiments, ifone mode is generating prediction samples according to a givenprediction direction (e.g., Planar or DC mode) this mode is called anon-angular mode. In some examples, each intra prediction mode isassociated with a mode number (also called intra prediction mode index).For example, in VVC, Planar, DC, horizontal, and vertical intraprediction modes are associated with mode number 0, 1, 18(INTRA_ANGULAR18) and 50 (INTRA_ANGULAR50), respectively.

According to some embodiments, the Planar and/or DC modes are enabledfor non-zero reference lines. The prediction process of Planar and/or DCmode may be dependent on the reference line index. In one embodiment,for the Planar prediction mode, the positions of top-right andbottom-left samples used in the Planar prediction process are the samefor different reference lines. For example, FIG. 10 illustrates acurrent block (1000) with reference lines Reference Line 0, ReferenceLine 1, Reference Line 2, and Reference Line 3. The above rows forReference Lines 0-3 are associated with samples A_0 to A_3,respectively. Furthermore, the rows to the left of current block (1000)for Reference Lines 0-3 are associated with samples B_0 to B_3,respectively. As illustrated in FIG. 10, samples A_0 and A_3 are locatedin the same position, and samples B_0 and B_3 are located in a sameposition.

In another embodiment, for the Planar prediction mode, differentreference lines use the same top-right and bottom-left samples for thePlanar prediction process. For example, the non-zero reference linesstill use the top-right and bottom-left samples used in thezero-reference line for the Planar prediction process.

According to some embodiments, the positions of the top-right andbottom-left samples used in the Planar prediction process are differentfor different reference lines. For example, as illustrated in FIG. 11,the samples A_0-A_3 for Reference Lines 0-3, respectively, are atdifferent positions for each reference line. Similarly, the samplesB_0-B_3 for Reference Lines 0-3, respectively, are at differentpositions for each reference line.

According to some embodiments, the positions of the top-right and thebottom-left samples used in the Planar prediction process are differentfor the zero reference line and non-zero reference lines. For example,as illustrated in FIG. 12 for current block (1200), the positions oftop-right (i.e., A_1-A_3) and bottom-left (i.e., B_1-B_3) samples usedin the Planar prediction process are the same for corresponding non-zeroreference lines (i.e., Reference Lines 1-3), respectively, but different(i.e., A_0 and B_0) with the zero reference line (i.e., Reference Line0).

According to some embodiments, Planar and/or DC prediction modes fornon-zero reference lines are converted to another angular predictionmode before the intra prediction process. For example, Planar and/or DCprediction modes are converted to another angular prediction mode byadding an offset value to one of the MPM list candidates. In anotherexample, Planar and/or DC prediction modes are converted to anotherdefault angular prediction mode, such as vertical, or horizontal, ordiagonal prediction modes.

According to some embodiments, the number (or positions) of referencesamples used for the DC prediction mode is dependent on the referenceline index. In one embodiment, for non-zero reference lines, up to tworeference samples are used for the calculating the DC prediction value.In another embodiment, for square blocks, only one sample from the leftside and one sample from the above side are used to calculate the DCvalue when a non-zero reference line index is signaled. In anotherembodiment, for non-square blocks, only one sample from the long side isused to calculate the DC value when a non-zero reference line index issignaled.

According to some embodiments, for non-zero reference lines, only onereference sample is used for the calculation of DC prediction. Forexample, for the non-zero reference lines, the position of a referencesample used for calculating the DC value is predefined and dependent onthe reference line index.

According to some embodiments, for non-square blocks, whether thereference samples used for calculating the DC value is from the shortside or long side is dependent on the reference line index. In oneexample, the reference samples from the short side are used forcalculating the DC value when a non-zero reference line index issignaled. In another example, the reference samples from the short sideare used for calculating the DC value when the signaled reference lineindex is 1, otherwise the reference samples from the long side are usedfor calculating the DC value. In some examples, the long side is usedwhen the zero reference line is indexed.

According to some embodiments, for all block shapes, only referencesamples from one side is used for calculating the DC values, and whetherto use the reference samples from the short side or long side isdependent on the block shape and/or reference line index. In oneexample, for the zero reference line, when the width of the currentblock is equal to or larger than the height of the current block, thereference samples in the above row is used to calculate the DC value.Otherwise, when the width of the current block is less than the heightof the current block, the reference samples in the left column is usedto calculate the DC value.

In another example, for non-zero reference lines, when the width of thecurrent block is equal to or larger than the height of current block,the reference samples in the left column is used to calculate the DCvalue. Otherwise, when the width of the current block is less than theheight of the current block, the reference samples in the above row isused to calculate the DC value.

FIG. 13 illustrates an embodiment of a process performed by a decodersuch as decoder (710). The process may start at step (S1300) where acoded video bitstream including a current block is retrieved. Theprocess proceeds to step (S1302) where a reference line index for thecurrent block is retrieved from the coded video bitstream. For example,the reference line index may refer to one of a plurality of referencelines such as Reference Lines 0-3 (FIG. 10).

The process proceeds to step (S1304) where it is determined if thecurrent block is encoded in the non-angular intra prediction mode suchas the Planar or DC prediction mode. If the current block is encoded inan angular intra prediction mode, the process proceeds to step (S1306)where the current block is decoded in accordance with the angular intraprediction mode with at least one reference sample from a reference lineindicated by the reference line index.

Returning to step (S1304), if the current block is encoded in anon-angular intra prediction mode, the process proceeds to step (S1308)where it is determined whether the reference line index indicates anon-zero reference line such as one of Reference Lines 1-3 (FIG. 10). Ifthe reference line index indicates a non-zero reference line, theprocess proceeds to step (S1310) where (i) the non-angular intraprediction modes for the non-zero reference line is enabled, and (ii)the current block is decoded in accordance with the non-angular intraprediction mode with at least one reference sample from the non-zeroreference line. If at step (S1308) the reference line index indicatesthe zero reference line, the process proceeds to step (S1312) where thecurrent block is decoded in accordance with the non-angular intraprediction mode with at least one sample from the zero reference line.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 14 shows a computersystem (1400) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 14 for computer system (1400) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1400).

Computer system (1400) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1401), mouse (1402), trackpad (1403), touchscreen (1410), data-glove (not shown), joystick (1405), microphone(1406), scanner (1407), camera (1408).

Computer system (1400) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1410), data-glove (not shown), or joystick (1405), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1409), headphones(not depicted)), visual output devices (such as screens (1410) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1400) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1420) with CD/DVD or the like media (1421), thumb-drive (1422),removable hard drive or solid state drive (1423), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1400) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1449) (such as, for example USB ports of thecomputer system (1400)); others are commonly integrated into the core ofthe computer system (1400) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1400) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1440) of thecomputer system (1400).

The core (1440) can include one or more Central Processing Units (CPU)(1441), Graphics Processing Units (GPU) (1442), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1443), hardware accelerators for certain tasks (1444), and so forth.These devices, along with Read-only memory (ROM) (1445), Random-accessmemory (1446), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1447), may be connectedthrough a system bus (1448). In some computer systems, the system bus(1448) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1448),or through a peripheral bus (1449). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1441), GPUs (1442), FPGAs (1443), and accelerators (1444) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1445) or RAM (1446). Transitional data can also be stored in RAM(1446), whereas permanent data can be stored for example, in theinternal mass storage (1447). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1441), GPU (1442), massstorage (1447), ROM (1445), RAM (1446), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1400), and specifically the core (1440) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1440) that are of non-transitorynature, such as core-internal mass storage (1447) or ROM (1445). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1440). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1440) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1446) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1444)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

(1) A method of video decoding performed in a video decoder, includesreceiving a coded video bitstream including a current block in a currentpicture; retrieving, from the coded video bitstream for the currentblock encoded in an intra prediction mode, a reference line indexindicating a reference line from a plurality of reference lines thatinclude a zero reference line, in which the zero reference linecomprises a closer reference line to the current block than each othernon-zero reference line in the plurality of reference lines; determiningwhether the current block is encoded in a non-angular intra predictionmode; in response to the block being encoded in the non-angular intraprediction mode, determining whether the reference line index indicatesa non-zero reference line from the plurality of reference lines; and inresponse to determining that the reference line index is the non-zeroreference line, (i) enabling non-angular intra prediction modes for thenon-zero reference line, and (ii) decoding the current block with atleast one reference sample from the non-zero reference line.

(2) The method according to feature (1), in which the non-angular intraprediction mode is the planar intra prediction mode.

(3) The method according to feature (2), in which each reference samplein the plurality of reference lines is located in a same position.

(4) The method of feature (2), in which each reference sample in theplurality of reference lines is located at a different position.

(5) The method according to feature (2), in which each reference samplein each non-zero reference line from the plurality of reference lines isat a different position than a reference sample in the zero referenceline.

(6) The method of feature (5), in which each reference sample in eachnon-zero reference line is at a same position with respect to eachother.

(7) The method of any one of features (1)-(6), further including inresponse to determining that the block is encoded in the non-angularintra prediction mode, converting the non-angular intra prediction modeto an angular prediction mode, in which the current block is decodedwith the angular prediction mode.

(8) The method of feature (6) or (7), in which the non-angular intraprediction mode is converted to one of a vertical intra prediction mode,a horizontal intra prediction mode, and a diagonal mode.

(9) The method of any one of features (1)-(8), in which the non-angularintra prediction mode is the DC prediction mode.

(10) The method of feature (9), in which a number of reference samplesis dependent on a value of the reference line index.

(11) The method of feature (9) or (10), in which the current block is anon-square block.

(12) The method of feature (11), in which in response to thedetermination that the reference line index is the non-zero referenceline, the at least one reference sample is from a short side of thecurrent block.

(13) The method of feature (11), in which in response to a determinationthat the reference line index is 1, the at least one reference sample isfrom a short side of the current block, and in which in response to adetermination that the reference line index is not 1, the at least onereference sample is from a long side of the current block.

(14) The method of feature (9), further including: in response todetermining that the reference line index is the zero reference line,determining whether the width of the current block is larger than aheight of the current block; in response to determining that the widthof the current block is equal to or larger than the height of thecurrent block, decoding the current block with at least one referencesample from the zero reference line from a row above the current block;and in response to determining that the width of the current block isless than the height of the current block, decoding the current blockwith at least one reference sample from the zero reference line from arow left of the current block.

(15) The method of feature (9), in response to determining that thereference line index is a non-zero reference line, determining whetherthe width of the current block is larger than a height of the currentblock; in response to determining that the width of the current block isequal to or larger than the height of the current block, the at leastone reference sample is from the non-zero reference line from a row leftof the current block; and in response to determining that the width ofthe current block is less than the height of the current block, the atleast one reference sample is from the non-zero reference line from arow above the current block.

(16) A video decoder for video decoding including circuitry configuredto receive a coded video bitstream including a current block in acurrent picture, retrieve, from the coded video bitstream for thecurrent block encoded in an intra prediction mode, a reference lineindex indicating a reference line from a plurality of reference linesthat include a zero reference line, in which the zero reference linecomprises a closer reference line to the current block than each othernon-zero reference line in the plurality of reference lines, determinewhether the current block is encoded in a non-angular intra predictionmode, in response to the block being encoded in the non-angular intraprediction mode, determine whether the reference line index indicates anon-zero reference line from the plurality of reference lines, and inresponse to a determination that the reference line index is thenon-zero reference line, (i) enable non-angular intra prediction modesfor the non-zero reference line, and (ii) decode the current block withat least one reference sample from the non-zero reference line.

(17) The video decoder of feature (16), in which the non-angular intraprediction mode is the planar intra prediction mode.

(18) The video decoder according to feature (17), in which eachreference sample in the plurality of reference lines is located in asame position.

(19) The video decoder of feature (17), in which each reference samplein the plurality of reference lines is located at a different position.

(20) A non-transitory computer readable medium having instructionsstored therein, which when executed by a processor in a video decodercauses the processor to execute a method including: receiving a codedvideo bitstream including a current block in a current picture;retrieving, from the coded video bitstream for the current block encodedin an intra prediction mode, a reference line index indicating areference line from a plurality of reference lines that include a zeroreference line, in which the zero reference line comprises a closerreference line to the current block than each other non-zero referenceline in the plurality of reference lines; determining whether thecurrent block is encoded in a non-angular intra prediction mode; inresponse to the block being encoded in the non-angular intra predictionmode, determining whether the reference line index indicates a non-zeroreference line from the plurality of reference lines; and in response todetermining that the reference line index is the non-zero referenceline, (i) enabling non-angular intra prediction modes for the non-zeroreference line, and (ii) decoding the current block with at least onereference sample from the non-zero reference line.

APPENDIX 1 - If (leftIntraDir == aboveIntraDir &&leftIntraDir >DC_IDX) - MPM [0] = leftIntraDir; (A1_1) - MPM [1] =((leftIntraDir + offset) % mod) + 2; (A1_2) - MPM [2] = ((leftIntraDir− 1) % mod) + 2; (A1_3) - Else if (leftIntraDir == aboveIntraDir) - MPM[0] = PLANAR_IDX; (A1_4) - MPM [1] = DC_IDX; (A1_5) - MPM [2] = VER_IDX;(A1_6) - Else if (leftIntraDir != aboveIntraDir) - MPM [0] =leftIntraDir; (A1_7) - MPM [1] = aboveIntraDir; (A1_8) - If(leftIntraDir > 0 && aboveIntraDir > 0) (A1_9) - MPM [2] = PLANAR_IDX;(A1_10) - Else - MPM [2] = (leftIntraDir + aboveIntraDir) < 2 ? VER_IDX: DC_IDX; (A1_11)

APPENDIX 2 - If candIntraPredModeB is equal to candIntraPredModeA andcandIntraPredModeA is  greater than INTRA_DC, candModeList[ x ] with x =0..5 is derivedas follows: - If IntraLumaRefLineIdx[ xCb ][ yCb ] isequal to 0, thefollowing applies: candModeList[ 0 ] = candIntraPredModeA (A2_4) candModeList[ 1 ] = INTRA_PLANAR  (A2_5) candModeList[ 2 ] =INTRA_DC (A2_6) candModeList[ 3 ] = 2 + ( ( candIntraPredModeA + 61 ) %64 )  (A2_7) candModeList[ 4 ] = 2 + ( ( candIntraPredModeA − 1 ) % 64 ) (A2_8) candModeList[ 5 ] = 2 + ( ( candIntraPredModeA + 60 ) % 64 ) (A2_9) - Otherwise (IntraLumaRefLineIdx[ xCb ][ yCb ] is not equal to0), the following  applies: candModeList[ 0 ] = candIntraPredModeA (A2_10) candModeList[ 1 ] = 2 + ( ( candIntraPredModeA + 61 ) % 64 ) (A2_11) candModeList[ 2 ] = 2 + ( ( candIntraPredModeA − 1 ) % 64 ) (A2_12) candModeList[ 3 ] = 2 + ( ( candIntraPredModeA + 60 ) % 64 ) (A2_13) candModeList[ 4 ] = 2 + ( candIntraPredModeA % 64)  (A2_14)candModeList[ 5 ] = 2 + ( ( candIntraPredModeA + 59 ) % 64 )  (A2_15) -Otherwise if candIntraPredModeB is not equal to candIntraPredModeA and candIntraPredModeA or candIntraPredModeB is greater than INTRA_DC, the following applies: - The variables minAB and maxAB are derived asfollows: minAB = candModeList[ (candModeList[ 0 ] > candModeList[ 1 ] )? 1 : 0 ]  (A2_16) maxAB = candModeList[ (candModeList[ 0 ] >candModeList[ 1 ] ) ? 0 : 1 ]  (A2_17) - If candIntraPredModeA andcandIntraPredModeB are both greater than  INTRA_DC, candModeList[ x ]with x = 0..5 is derived asfollows: candModeList[ 0 ] =candIntraPredModeA  (A2_18) candModeList[ 1 ] = candIntraPredModeB (A2_19) - If IntraLumaRefLineIdx[ xCb ][ yCb ] is equal to 0,thefollowing applies: candModeList[ 2 ] = INTRA_PLANAR  (A2_20)candModeList[ 3 ] = INTRA_DC  (A2_21)  - If maxAB − minAB is in therange of 2 to 62, inclusive, the following  applies: candModeList[ 4 ] =2 + ( ( maxAB + 61 ) % 64 )  (A2_22) candModeList[ 5 ] = 2 + ( ( maxAB −1 ) % 64 )  (A2_23)  - Otherwise, the following applies: candModeList[ 4] = 2 + ( ( maxAB + 60 ) % 64 )  (A2_24) candModeList[ 5 ] = 2 + ( (maxAB ) % 64)  (A2_25) - Otherwise (IntraLumaRefLineIdx[ xCb ][ yCb ] isnot equal to 0), the  following applies:  - If maxAB − minAB is equal to1, the following applies: candModeList[ 2 ] = 2 + ( ( minAB + 61 ) % 64)  (A2_26) candModeList[ 3 ] = 2 + ( ( maxAB − 1 ) % 64 )  (A2_27)candModeList[ 4 ] = 2 + ( ( minAB + 60 ) % 64 )  (A2_28) candModeList[ 5] = 2 + ( maxAB % 64)  (A2_29)  - Otherwise if maxAB − minAB is equal to2, the following applies: candModeList[ 2 ] = 2 + ( ( minAB − 1 ) % 64 ) (A2_30) candModeList[ 3 ] = 2 + ( ( minAB + 61 ) % 64 )  (A2_31)candModeList[ 4 ] = 2 + ( ( maxAB − 1 ) % 64 )  (A2_32) candModeList[ 5] = 2 + ( ( minAB + 60 ) % 64 )  (A2_33)  - Otherwise if maxAB − minABis greater than 61, the following applies: candModeList[ 2 ] = 2 + ( (minAB − 1 ) % 64 )  (A2_34) candModeList[ 3 ] = 2 + ( ( maxAB + 61 ) %64 )  (A2_35) candModeList[ 4 ] = 2 + ( minAB % 64 )  (A2_36)candModeList[ 5 ] = 2 + ( ( maxAB + 60 ) % 64 )  (A2_37)  - Otherwise,the following applies: candModeList[ 2 ] = 2 + ( ( minAB + 61 ) % 64 ) (A2_38) candModeList[ 3 ] = 2 + ( ( minAB − 1 ) % 64 )  (A2_39)candModeList[ 4 ] = 2 + ( ( maxAB + 61 ) % 64 )  (A2_40) candModeList[ 5] = 2 + ( ( maxAB − 1 ) % 64 )  (A2_41) - Otherwise (candIntraPredModeAor candIntraPredModeB is greater than  INTRA_DC), candModeList[ x ] withx = 0..5 is derived asfollows: - If IntraLumaRefLineIdx[ xCb ][ yCb ] isequal to 0, the following applies: candModeList[ 0 ] =candIntraPredModeA  (A2_42) candModeList[ 1 ] = candIntraPredModeB (A2_43) candModeList[ 2 ] = 1 − minAB  (A2_44) candModeList[ 3 ] = 2 +( ( maxAB + 61 ) % 64 )  (A2_45) candModeList[ 4 ] = 2 + ( ( maxAB − 1 )% 64 )  (A2_46) candModeList[ 5 ] = 2 + ( ( maxAB + 60 ) % 64 ) (A2_47) - Otherwise (IntraLumaRefLineIdx[ xCb ][ yCb ] is not equal to0), the  following applies: candModeList[ 0 ] = maxAB  (A2_48)candModeList[ 1 ] = 2 + ( ( maxAB + 61 ) % 64 )  (A2_49) candModeList[ 2] = 2 + ( ( maxAB − 1 ) % 64 )  (A2_50) candModeList[ 3 ] = 2 + ( (maxAB + 60 ) % 64 )  (A2_51) candModeList[ 4 ] = 2 + ( maxAB % 64 ) (A2_52) candModeList[ 5 ] = 2 + ( ( maxAB + 59 ) % 64 )  (A2_53) -Otherwise, the following applies: - If IntraLumaRefLineIdx[ xCb ][ yCb ]is equal to 0, the following applies: candModeList[ 0 ] =candIntraPredModeA  (A2_54) candModeList[ 1 ] = ( candModeList[0] ==INTRA_PLANAR ) ? INTRA_DC :  (A2_55) INTRA_PLANAR candModeList[ 2 ] =INTRA_ANGULAR50  (A2_56) candModeList[ 3 ] = INTRA_ANGULAR18  (A2_57)candModeList[ 4 ] = INTRA_ANGULAR46  (A2_58) candModeList[ 5 ] =INTRA_ANGULAR54  (A2_59) - Otherwise (IntraLumaRefLineIdx[ xCb ][ yCb ]is not equal to 0), the following  applies: candModeList[ 0 ] =INTRA_ANGULAR50  (A2_60) candModeList[ 1 ] = INTRA_ANGULAR18  (A2_61)candModeList[ 2 ] = INTRA_ANGULAR2  (A2_62) candModeList[ 3 ] =INTRA_ANGULAR34  (A2_63) candModeList[ 4 ] = INTRA_ANGULAR66  (A2_64)candModeList[ 5 ] = INTRA_ANGULAR26  (A2_65)

What is claimed is:
 1. A method of video decoding performed in a videodecoder, comprising: receiving a coded video bitstream including acurrent block in a current picture; retrieving, from the coded videobitstream for the current block encoded in an intra prediction mode, areference line index indicating a reference line from a plurality ofreference lines that include a zero reference line, wherein the zeroreference line comprises a closer reference line to the current blockthan each other non-zero reference line in the plurality of referencelines; determining whether the current block is encoded in a non-angularintra prediction mode; in response to the block being encoded in thenon-angular intra prediction mode, determining whether the referenceline index indicates a non-zero reference line from the plurality ofreference lines; and in response to determining that the reference lineindex is the non-zero reference line, (i) enabling non-angular intraprediction modes for the non-zero reference line, and (ii) decoding thecurrent block with at least one reference sample from the non-zeroreference line.
 2. The method according to claim 1, wherein thenon-angular intra prediction mode is the planar intra prediction mode.3. The method according to claim 2, wherein each reference sample in theplurality of reference lines is located in a same position.
 4. Themethod of claim 2, wherein each reference sample in the plurality ofreference lines is located at a different position.
 5. The methodaccording to claim 2, wherein each reference sample in each non-zeroreference line from the plurality of reference lines is at a differentposition than a reference sample in the zero reference line.
 6. Themethod of claim 5, wherein each reference sample in each non-zeroreference line is at a same position with respect to each other.
 7. Themethod of claim 1, further comprising in response to determining thatthe block is encoded in the non-angular intra prediction mode,converting the non-angular intra prediction mode to an angularprediction mode, wherein the current block is decoded with the angularprediction mode.
 8. The method of claim 6, wherein the non-angular intraprediction mode is converted to one of a vertical intra prediction mode,a horizontal intra prediction mode, and a diagonal mode.
 9. The methodof claim 1, wherein the non-angular intra prediction mode is the DCprediction mode.
 10. The method of claim 9, wherein a number ofreference samples is dependent on a value of the reference line index.11. The method of claim 9, wherein the current block is a non-squareblock.
 12. The method of claim 11, wherein in response to thedetermination that the reference line index is the non-zero referenceline, the at least one reference sample is from a short side of thecurrent block.
 13. The method of claim 11, wherein in response to adetermination that the reference line index is 1, the at least onereference sample is from a short side of the current block, and whereinin response to a determination that the reference line index is not 1,the at least one reference sample is from a long side of the currentblock.
 14. The method of claim 9, further comprising: in response todetermining that the reference line index is the zero reference line,determining whether the width of the current block is larger than aheight of the current block; in response to determining that the widthof the current block is equal to or larger than the height of thecurrent block, decoding the current block with at least one referencesample from the zero reference line from a row above the current block;and in response to determining that the width of the current block isless than the height of the current block, decoding the current blockwith at least one reference sample from the zero reference line from arow left of the current block.
 15. The method of claim 9, in response todetermining that the reference line index is a non-zero reference line,determining whether the width of the current block is larger than aheight of the current block; in response to determining that the widthof the current block is equal to or larger than the height of thecurrent block, the at least one reference sample is from the non-zeroreference line from a row left of the current block; and in response todetermining that the width of the current block is less than the heightof the current block, the at least one reference sample is from thenon-zero reference line from a row above the current block.
 16. A videodecoder for video decoding, comprising: circuitry configured to: receivea coded video bitstream including a current block in a current picture,retrieve, from the coded video bitstream for the current block encodedin an intra prediction mode, a reference line index indicating areference line from a plurality of reference lines that include a zeroreference line, wherein the zero reference line comprises a closerreference line to the current block than each other non-zero referenceline in the plurality of reference lines, determine whether the currentblock is encoded in a non-angular intra prediction mode, in response tothe block being encoded in the non-angular intra prediction mode,determine whether the reference line index indicates a non-zeroreference line from the plurality of reference lines, and in response toa determination that the reference line index is the non-zero referenceline, (i) enable non-angular intra prediction modes for the non-zeroreference line, and (ii) decode the current block with at least onereference sample from the non-zero reference line.
 17. The video decoderof claim 16, wherein the non-angular intra prediction mode is the planarintra prediction mode.
 18. The video decoder according to claim 17,wherein each reference sample in the plurality of reference lines islocated in a same position.
 19. The video decoder of claim 17, whereineach reference sample in the plurality of reference lines is located ata different position.
 20. A non-transitory computer readable mediumhaving instructions stored therein, which when executed by a processorin a video decoder causes the processor to execute a method comprising:receiving a coded video bitstream including a current block in a currentpicture; retrieving, from the coded video bitstream for the currentblock encoded in an intra prediction mode, a reference line indexindicating a reference line from a plurality of reference lines thatinclude a zero reference line, wherein the zero reference line comprisesa closer reference line to the current block than each other non-zeroreference line in the plurality of reference lines; determining whetherthe current block is encoded in a non-angular intra prediction mode; inresponse to the block being encoded in the non-angular intra predictionmode, determining whether the reference line index indicates a non-zeroreference line from the plurality of reference lines; and in response todetermining that the reference line index is the non-zero referenceline, (i) enabling non-angular intra prediction modes for the non-zeroreference line, and (ii) decoding the current block with at least onereference sample from the non-zero reference line.